1. Background of the Invention
The invention relates generally to the enhanced removal of aerosols, such as fine liquid droplets, and particulate matter from a gas stream. More specifically, the invention is directed to the removal of aerosols and particulate matter, and in some embodiments a vapor phase contaminant, from the flue gas of a combustion system.
2. Description of Related Art
The emission of aerosols, such as particulate matter or fly ash and acid mist, from flue gas generated by utility power plants is an important issue. Several technologies have been used to remove such aerosols including wet and dry electrostatic precipitators, wet and dry scrubbers, and baghouses. However, these existing collectors are required to handle even higher amounts of aerosols as more materials such as sorbents for mercury and acid gas control are being injected into the flue gas stream and new pollution control devices such as selective reduction (SCR) catalysts increase sulfuric acid mist formation. The increased aerosol loading leads to increased stack particulate and acid mist emissions. In addition, environmental regulations are becoming increasingly more stringent, requiring power plants to reduce stack aerosol emissions even further. Therefore, it is desirable to improve and enhance the methods and equipment currently used for removing aerosols, including particulate matter or fly ash and acid mists, from gas streams. In particular, there is a need for methods and apparatuses or “polishers” that supplement the removal of particulate matter or fly ash obtained using traditional equipment.
In addition, special attention has been given to emissions of vaporous trace contaminants, such as mercury (Hg), in flue gas generated by utility power plants and the impact such trace contaminants may have on the environment. Generally, trace contaminants include those vaporous chemical species present in relatively low concentrations in a given gas stream. For example, mercury is present in flue gas from a fossil-fuel-fired combustion system in very low concentrations (<1 ppm) and forms a number of volatile compounds that are difficult to remove. Specially designed and costly emissions-control systems are required to effectively capture these trace amounts of mercury. Therefore, there is a need to improve the methods and equipment used for removing such vaporous trace contaminants from gas streams.